The convolutions of the external ear, particularly the concha, act to increase or decrease the amplitude of different frequency components of a sound as it passes from the free field to the eardrum.

The points are found, explains Sara, by imagining a baby in an inverted foetal position, with the earlobe representing the head, the concha the internal organs and so on.

In the majority of cases there is a combination of too much cartilage in the central bowl shaped portion of the ear called the concha, and a failure of the natural folds to develop in the portion of the ear known as the antihelix.